Alkali metal quaternary chalcogenides and process for the preparation thereof

ABSTRACT

Alkali metal quaternary chalcogenides and process for the preparation. The chalcogenides have the formula A x  B y  C z  D n  containing (CD 4 ) 4-   or (C 2  D 6 ) 4-   ions where A is selected from the group consisting of an alkali metal and a mixture of alkali metals, B is selected from the group consisting of mercury, zinc and manganese, C is a metal selected from the group consisting of germanium and tin and D is selected from the group consisting of sulfur and selenium, wherein x, y, z and n are molar amounts which provide non-linear optical transmission properties. These chalcogenides are useful as non-linear optical transmission crystals.

This is a divisional of application Ser. No. 08/298,620 filed on Aug. 31, 1994 now U. S. Pat. No. 5,531,936.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The present invention relates to novel alkali metal quaternary chalcogenides containing (CD₄)⁴⁻ or (C₂ D₆)⁴⁻ ions, wherein C is germanium or tin and D is S or Se, and the process for the preparation of such compounds using molten fused salts. In particular, the present invention relates to such chalcogenides having non-linear optical transmission properties.

(2) Description of Related Art

From the structural point of view, quaternary chalcogenides are interesting due to their structural varieties resulting from the combination in different ratios of two kinds of metal centers with different size, coordination preference and arrangement. Alkali earth metal containing quaternary chalcogenides have been extensively investigated using high temperature solid state synthesis (a) Teske, Chr. L. Z., Anorg. Allg. Chem. 445:193-201 (1978); (b) Teske, Chr. L., Vetter, O. Z., Anorg. Allg. Chem. 427:200-204 (1976); (c) Teske, Chr. L. Z., Naturforsch 35b:7-11 (1980); (d) Teske, Chr. L. Z., Anorg. Allg. Chem., 419:67-76 (1976); (e) Teske, Chr. L., Vetter, O. Z., Anorg. Allg. Chem. 426:281-287 (1976); (f) Teske, Chr. L. Z., Anorg. Allg. Chem. 460:163-168 (1980); (g) Teske, Chr. L. Z. , Anorg. Allg. Chem. 522:122-130 (1985); (h) Teske, Chr. L. Z., Naturforsch 35b:509-510 (1980); (i) Teske, Chr. L. Z., Naturforsch, 34b:544-547 (1979)). Recently molten alkali metal salts have been proven to be convenient reaction media for chalcogenide synthesis at lower temperature regimes (<500° C.). So far, most of the research has focused on ternary systems ((a) Kanatzidis, M. G., Chem. Mater. 2:353-363 (1990); (b) Sunshine, S., et al., J. Am. Chem. Soc. 109: 6202-6204 (1987 ); (c) Kanatzidis, M. G., et al., J. Am. Chem. Soc. 111:3767-3769 (1989); (d) Liao, J. -H., et al., Inorg. Chem. 32:2453-2462 (1993); (e) Park, Y., et al., Angew. Chem. Int. Ed. Engl. 29:914-915 (1990); (f) Park, Y., et al., Angew. Chem. Int. Ed. Engl. 30:1325-1328 (1991); (g) Kanatzidis, M. G., et al., Chem. Mater. 2:99-101 (1990); (h) Kanatzidis, M. G., et al., Chem. Mater. 2:353-363 (1990); (i) Park, Y., Dissertation, Michigan State University (1992 )). Less effort has been expended on quaternary chalcogenides ((a) Keane, P. M., et al., Acc. of Chem. Res., 24:223-229 (1991); (b) Lu, Y. -J, et al., Inorg. Chem. 30:3317-3320 (1991); (c) Lu, Y. -J., et al., J. Solid State Chem. 98:312-317 (1992); (d) Wu, P., et al., J. Solid State Chem. 97:383-390 (1992)).

A series of alkali metal mixed Sn/Cu or Au quaternary chalcogenides have been reported (Liao, J. -H, et al., Chem. Mater. 5:1561-1569 (1993)) . Molten salt techniques have been shown to be promising for synthesizing quaternary chalcogenides. Alkali metal salts with (SnS₄)⁴⁻ and/or (Sn₂ S₆)⁴⁻ have been characterized ((a) Susa, K., et al., J. Solid State Chem. 3:75-82 (1971); (b) Jumas, J. C., et al., Cryst. Struct. Comm. 2:157 (1973); (c) Schiwy, W., et al., Anorg. Allg. Chem. 402:77-86 (1973); (d) Krebs, B., et al., Anorg. Allg. Chem. 393:241-252 (1972)). The germanium analogs are well known ((a) Olivier-Fourcade, J., et al., Rev. Chim. Miner. 9:757-770 (1972); (b) Eisenmann, B., et al., Anorg. Allg. Chem., 516:49-54 (1984); (c) Pohl, S., et al., Naturforsch 28b:565 (1973); (d) Kreb, B., et al., Angew. Chem. Int. Ed. Engl. 9:897 (1970); (e) Kreb, B., et al., Naturforsch 26b:853-854 (1971); (f) Pohl, S., et al., Anorg. Allg. Chem. 424:265-272 (1976); (g) Philippot, E., et al., Rev. Chim. Miner. 8:477-489 (1971)) and have been found as building blocks in the structures of KInGeS₄, KGaGeS₄ ^(3d) and BaAg₂ GeS₄ (Teske, Chr., L. Z. Naturforsch 34b:544-547 (1979)). Mixed metal systems of divalent metals (Zn, Hg, Mn) and main group metals (Ge, Sn) have not been described.

U.S. Pat. No. 3,124,426 to Offergeld et al describes photo resistive indium compositions including chalcogenides.

U.S. Pat. No. 3,480,409 to Dillon et al describes crystalline CdCr₂ Se₄ crystals which are ferromagnetic and thus are useful for magneto-optic modulation.

U.S. Pat. No. 3,696,038 to Davies et al describes Ag₃ AsS₃ chalcogenide crystals as non-linear light transmission devices.

U.S. Pat. No. 3,688,109 to Gamble describes the use of heavy metal chalcogenides as X-ray gratings. The Bragg's law d-spacing is between 6 and 24Å.

U.S. Pat. No. 3,803,044 to Carnall et al describe polycrystalline chalcogenide compounds which are magneto-optical of the formula ACr₂ X₄ where X is a chalcogen anion (S, Te, Se) and A is a Group IA to IVA and IB to VIIIB element.

U.S. Pat. No. 4,258,109 to Liang et al describes chalcogenide compounds used as cathodes.

U.S. Pat. No. 4,366,141 to Martin et al describes the preparation of chalcogenides which are polycrystalline and have improved transmission in the visible and infrared light regions.

U.S. Pat. No. 4,730,896 to Katsuyama et al describes ternary chalcogenide glass (amorphous non-crystalline) compounds of Ge-Se-Te which are capable of transmitting infra-red rays of 2 μm or larger.

U.S. Pat. No. 4,751,022 to Sugio et al describes chalcogenide compounds which are oxy acid salts which are used for humidity sensing.

U.S. Pat. No. 4,789,500 to Morimoto et al describes magneto-optical Cd_(1-x) Mn_(x) Te where X is 0.01≧x≧0.99.

Kanatzidis, M. G., Chem. of Materials 2 353-363 (1990) describes the preparation of various ternary chalcogenide polychalcogenide compounds using a molten salt method at 200°-450° C.

Liao et al, Inorganic Chem 32 2453-2462 (1993) describe the use of the molten salt technique to prepare various ternary polychalcogenides.

Voevodina, O. V., et al Zhurnal Neorganicheskoi Khimii 37, 2776-2779 (1992) describe the preparation of ternary chalcogenides using the molten salt method.

Haeuseler et al, Z. Naturforsch, 44b:1035-1036 (1989) describe quaternary chalcogenides of the type Ag₂ HgMX₄. There is no description in this reference of alkali metal quaternary chalcogenides.

OBJECTS

It is therefore an object of the present invention to provide novel alkali metal chalcogenide compounds which have non-linear optical properties. Further, it is an object of the present invention to provide a fused salt method for producing such compounds. These and other objects will become increasingly apparent by reference to the following description and the drawings.

IN THE DRAWINGS

FIG. 1 is a ORTEP representation and labeling scheme of K₂ Hg₃ Sn₂ S₈ or K₂ Hg₃ Ge₂ S₈ viewed down the b-axis.

FIG. 2 is an ORTEP representation and labeling scheme of K₂ Hg₃ Sn₂ S₈ or K₂ Hg₃ Ge₂ S₈ viewed down the <110> direction.

FIG. 3 is an ORTEP representation and labeling scheme of K₆ Zn₄ Sn₅ S₁₇ viewed down the c-axis.

FIG. 4 is a representation of a (Zn₄ Sn₄ S₁₇)¹⁰⁻ cluster, which is the building block of K₆ Zn₄ Sn₅ S₁₇.

FIG. 5 is an ORTEP representation and labeling scheme of K₆ Zn₄ Sn₅ S₁₇ viewed down the a- or b-axis. This view shows the polar character of the structure. K(1) cations are located inside the wide and narrow tunnels parallel to a- or b-axis.

FIG. 6 is an ORTEP representation and labeling scheme of K₆ Zn₄ Sn₅ S₁₇ viewed down the <110> or <110> direction. K(2) and K(3) are located inside the tunnels.

FIG. 7A is an ORTEP representation and labeling scheme of (A) Rb₂ ZnSn₂ S₆ and FIG. 7B is the ORTEP representation of Cs₂ MnSn₂ S₆.

FIG. 8 is a representation of a single layer of the (MSn₂ S₆)²⁻ (M=Zn or Mn) framework viewed down the b-axis where adjacent layers above and below are related according to P2₁ symmetry.

FIGS. 9A and 9B are graphs showing the relationships of magnetization vs. applied magnetic field for Cs₂ MnSn₂ S₆ at 5° K. (FIG. 9A) and 300° K. (FIG. 9B).

FIGS. 10A and 10B are graphs showing the relationship of 1/χ_(m) vs. T which shows paramagnetism of Cs₂ MnSn₂ S₆ above T_(N) =9° K.

FIGS. 11A to 11E are optical absorption spectra of K₂ Hg₃ Sn₂ S₈ (FIG. 11A), K₂ Hg₃ Ge₂ S₈ (FIG. 11B), K₆ Zn₄ Sn₅ S₁₇ (FIG. 11C), Rb₂ ZnSn₂ S₆ (FIG. 11D, Cs₂ MnSn₂ S₆ (FIG. 11E).

FIGS. 12A to 12E are infrared spectra of K₂ Hg₃ Sn₂ S₈ (FIG. 12A) , K₂ Hg₃ Ge₂ S₈ (FIG. 12B), K₆ Zn₄ Sn₅ S₁₇ (FIG. 12C), Rb₂ ZnSn₂ S₆ (FIG. 12D), Cs₂ MnSn₂ S₆ (FIG. 12E).

FIGS. 13 and 14 are side by side ORTEP representations of K₂ Hg₃ Ge₂ S₈ and (KRb)Hg₃ Ge₂ S₈.

GENERAL DESCRIPTION

The present invention relates to a crystalline alkali metal quaternary chalcogenide of the formula A_(x) B_(y) C_(z) D_(n) containing (CD₄)⁴⁻ or (C₂ D₆)⁴⁻ ions where A is selected from the group consisting of an alkali metal and a mixture of alkali metals, B is selected from the group consisting of mercury, zinc and manganese, C is a metal selected from the group consisting of germanium and tin and D is selected from the group consisting of sulfur and selenium, wherein x, y, z and n are molar amounts which provide non-linear optical transmission properties.

The present invention also relates to a chalcogenide compound having the empirical formula:

    A.sub.x B.sub.y C.sub.z D.sub.n

wherein A is selected from the group consisting of an alkali metal and a mixture of alkali metals, B is selected from the group consisting of mercury, zinc and manganese, C is a metal selected from the group consisting of germanium and tin and D is selected from the group consisting of sulfur and selenium, and wherein x is a number selected from the group consisting of 2 and 6, y is a number selected from the group consisting of 1, 3 and 4, z is a number selected from the group consisting of 2 and 5 and n is a number selected from the group consisting of 6, 8 and 17.

Further the present invention relates to a process for preparing a chalcogenide compound having the empirical formula

    A.sub.x B.sub.y C.sub.z D.sub.n

wherein A is selected from the group consisting of an alkali metal and a mixture of alkali metals, B is selected from the group consisting of mercury, zinc and manganese, C is a metal selected from the group consisting of germanium and tin and D is selected from the group consisting of sulfur and selenium, and wherein x is a number selected from the group consisting of 2 and 6, y is a number selected from the group consisting of 1, 3 and 4, z is a number selected from the group consisting of 2 and 5 and n is a number selected from the group consisting of 6, 8 and 17, which comprises reacting in a molten mixture ingredients selected from the group consisting of the B as an element, the C as an element, the A and the D together as an alkali metal sulfide and the B and the D together as a metal sulfide in molar amounts of the x, y, z or n and to produce the chalcogenide compound.

Further still, the present invention relates to a method including transmission of light through a crystal for analytical purposes, the improvement which comprises transmitting the light in a visible light and infrared light range between 0.4 and 20 μm through a crystal of a chalcogenide compound having the formula:

    A.sub.x B.sub.y C.sub.z D.sub.n

wherein A is selected from the group consisting of an alkali metal and a mixture of alkali metals, B is selected from the group consisting of mercury, zinc and manganese, C is a metal selected from the group consisting of germanium and tin and D is selected from the group consisting of sulfur and selenium, and wherein x is a number selected from the group consisting of 2 and 6, y is a number selected from the group consisting of 1, 3 and 4, z is a number selected from the group consisting of 2 and 5 and n is a number selected from the group consisting of 6, 8 and 17, wherein the light into the crystal and the light out of the crystal change frequency.

Finally the present invention relates to an apparatus for converting a first light to a second light of another frequency using a chalcogenide compound to make the conversion, the improvement which comprises providing in the apparatus a chalcogenide compound of the formula A_(x) B_(y) C_(z) D_(n) where A is selected from the group consisting of an alkali metal and a mixture of alkali metals, B is selected from the group consisting of mercury, zinc and manganese, C is a metal selected from the group consisting of germanium and tin and Dn is selected from the group consisting of sulfur and selenium, wherein x, y, z and n are molar amounts which provide non-linear optical transmission properties.

The following Examples 1 to 5 describe the preparation of the preferred chalcogenide compounds of the present invention. The reagents were: Sn metal: ˜325 mesh, 99.8% purity; -325 mesh, 99.5% purity, Ge metal: -100 mesh, 99.99% purity; Mn metal: 99.9% purity, -50 mesh, Aldrich Chemical Company, Inc., Milwaukee, Wis. Sublimed sulfur: 99.5˜100.5%; Zn powder: purified; HgS powder; J. T. Baker Inc., Phillipsburg, N.J. A₂ Q (A=K, Rb, Cs; Q=S, Se) starting materials were prepared as described elsewhere (Klemm, W., et al., Z. Anorg. Allg. Chem. 241:281-304 (1939)).

PHYSICAL MEASUREMENTS

The instruments and experimental setups for Infrared spectroscopy, SEM/EDS quantitative microprobe analysis and UV/vis/near-IR optical diffuse spectroscopy are well known.

Magnetic susceptibility data were collected on a Quantum Design SQUID system, Michigan State University, East Lansing, Mich. 34.98-mg (0.0466 mmol) of Cs₂ MnSn₂ S₆ was loaded in a plastic bag and purged with Ar gas before measurement. The sample of this compound included a small amount MnS impurity (<1%) which did not significantly influence the results. The diamagnetic contribution of the plastic bag was relatively small and was ignored during data processing. Measurements of magnetization versus applied magnetic field were performed from 50 Gauss to 5000 Gauss at both 5° K. and 300° K. for Cs₂ MnSn₂ S₆. Various temperature magnetic susceptibility data were collected at a magnetic field of 5000 Gauss with an ascending temperature ramp from 5° K. to 300° K.

EXAMPLE 1 K₂ Hg₃ Sn₂ S₈ (I)

A mixture of Sn powder (0. 030 g, 0.25 mmol), HgS powder (0.116 g, 0.499 mmol), K₂ S (0.055 g, 0.50 mmol) and S (0.128 g, 4.00 mmol) was heated at 400° C. for 4 days and was then cooled to room temperature at 4° C./hour. The product was washed with degassed dimethyl formamide (DMF) and was dried with acetone and ether. Yellow crystals of (I) and small amount of orange brown square planar crystals and red HgS crystals (less than 5%) were obtained. The yield of yellow crystals was 0.101 g (69% based on Sn). The yellow crystals are insoluble in water and common organic solvents. SEM/EDS semiquantitative elemental analyses indicated K₁.0 Sn₁.0 Hg₁.9 S₆.7.

EXAMPLE 2 K₂ Hg₃ Ge₂ S₈ (II)

The reaction of Ge(0.018 g, 0.25 mmol), HgS (0.087 g, 0.38 mmol), K₂ S (0.055 g, 0.50 mmol) and S (0.128 g, 4.00 mmol) at 400° C. for 4 days upon a cooling rate of 4° C./hour afforded yellow crystals of (II) and very small amount of HgS crystals. The yield of (II) was 0.083 g (64%, based on Ge). The product is stable in air and insoluble in water and common organic solvents. SEM/EDS indicated K₀.76 Hg₁.0 Ge₀.29 S₄.97.

EXAMPLE 3 K₆ Zn₄ Sn₅ S₁₇ (III)

The reaction of Sn (0. 059 g, 0.5 mmol), Zn (0.033 g, 0.5 mmol), K₂ S (0.110 g, 1.0 mmol) and S (0.256 g, 8.0 mmol) at 400° C. for 4 days upon a cooling rate of 4° C./hour afforded 0.068 g yellowish white crystals in ˜33% yield (based on Sn). The product was washed with degassed DMF and was dried with acetone and ether. The yield can be increased by adding more Sn metal in the reactions. The ratio of 6/5:4/5:2:16 (Sn:Zn:K₂ :S:S) under the same reaction condition gave a yield of ˜80%. However, this reaction also gave a small amount of yellowish orange crystals of K₂ Sn₂ S₅ and reddish orange crystals of K₂ Sn₂ S₈ as by-products. The yellowish white crystals of (III) are stable in air and insoluble in water and common organic solvents. SEM/EDS semiquantitative elemental analysis indicated K₂.3 Zn₁.0 Sn₁.75 S₇.38.

EXAMPLE 4 Rb₂ ZnSn₂ S₆ (IV)

The reaction of Sn (0.119 g, 1.00 mmol), Zn (0.033 g, 0.50 mmol), Rb₂ S (0.406 g, 1.00 mmol) and S (0.512 g, 8.00 mmol) at 400° C. for 4 days upon a cooling rate of 4° C./hour afforded 0.131-g brownish orange crystals of (IV) in ˜40% yield (based on Sn). The product was washed with degassed DMF, was dried with acetone and ether. The brownish white crystals are insoluble in water and common organic solvents. SEM/EDS semiquantitative elemental analysis indicated Rb₁.1 Zn₁.0 Sn₁.9 S₆.0.

EXAMPLE 5

Cs₂ MnSn₂ S₆ (V)

The reaction of Sn powder (0.072 g, 0.61 mmol), Mn powder (0.016 g, 0.29 mmol), Cs₂ S (0.358 g, 1.20 mmol) and S (0.154 g, 4.81 mmol) at 400° C. for 4 days upon a cooling rate of 4° C./hour gave 0.083-g brownish white crystals of (V) and very small amount of MnS powder. The yield of (V) is ˜38% yield (based on Sn). The product was washed with degassed DMF, was dried with acetone and ether. The brownish white crystals are insoluble in water and common organic solvents. SEM/EDS semiquantitative elemental analysis indicated Cs₂.6 Mn₁.0 Sn₂.8 S₁₀.2.

In Examples 1 to 5, x-ray powder diffraction patterns were used for the purpose of phase characterization and identification. The x-ray powder diffraction patterns were recorded with a Phillips XRD-3000 controlled by PDP 11 computer and operating at 40 kV/35 mA. Ni-filtered Cu radiation was used. In order to ensure the homogeneity, d-spacings obtained from x-ray powder diffraction (XRD) measurements of the products were compared with, and found to be identical, with those calculated from using the atomic coordinates determined from the single crystal data. The calculation of d-spacings was performed using the POWD 10⁸ program.

The single crystal x-ray diffraction data of chalcogenide compounds (II), (III) and (IV) were collected on a Rigaku AFC6S four-circle diffractometer while the data for (I) and (V) were collected on a Niclolet P3 diffractometer. Graphite monochromated Mo Kα radiation was used. All the crystals were mounted at the end of glass fibers. The stability of the experimental setup and crystal integrity were monitored by measuring three standard reflections periodically every 150 reflections for all the data set except for (I) which was monitored every 300 reflections. No significant decay was observed during the data collections. The structures were solved with direct methods (SHELXS-86)⁹, and were refined by a full-matrix least-square technique available in the TEXSAN¹⁰ programs running on a VAXstation 3100/76 computer. An empirical absorption correction was applied to all the data (based on ψ scans). An additional absorption correction following the DIFABS¹¹ procedure was applied to isotropically refined data. Since chalcogenide compounds (I)˜(V) crystallize in acentric space groups, their enantiomorphs were checked. The refinement of the enantiomorphous models of all compounds did not show significant improvement while the R/Rw values for chalcogenides (I)˜(IV) dropped from 5.1/5.1 to 3.9/4.2, from 4.9/6.6 to 4.3/5.9, from 4.3/5.4 to 3.6/4.6 and from 3.6/4.7 to 2.7/3.4, respectively. The models with lower R/Rw values and smaller standard deviation of bond distances and angles are reported.

The crystallographic data and detailed information of structure solution and refinement are listed in Table 1. Atomic coordinates and equivalent isotropic thermal parameters are given in Tables 2-6, respectively.

                  TABLE 1                                                          ______________________________________                                         Summary of Crystallographic Data for K.sub.2 Hg.sub.3 Sn.sub.2 S.sub.8         (I),                                                                           K.sub.2 Hg.sub.3 Ge.sub.2 S.sub.8 (II), K.sub.6 Zn.sub.4 Sn.sub.5              S.sub.17 (III), Rb.sub.2 ZnSn.sub.2 S.sub.6 (IV),                              Cs.sub.2 MnSn.sub.2 S.sub.6 (V).                                               ______________________________________                                                (I)       (II)        (III)                                             ______________________________________                                         formula  K.sub.2 Hg.sub.3 Sn.sub.2 S.sub.8                                                          K.sub.2 Hg.sub.3 Ge.sub.2 S.sub.8                                                          K.sub.6 Zn.sub.4 Sn.sub.5 S.sub.17            fw       1173.83     1081.63     1634.58                                       a, Å 19.522(5)   19.188(3)   13.796(2)                                     b, Å 9.835(3)    9.618(2)    13.796(2)                                     c, Å 8.431(2)    8.328(5)    9.580(2)                                      α  90.0        90.0        90.0                                          β   90.0        90.0        90.0                                          γ  90.0        90.0        90.0                                          Z, V, Å.sup.3                                                                       4,1618.7(9) 4,1537(1)   2,1823.3(6)                                   space group                                                                             Aba2(#41)   Aba2(#41)   I4m2(#119)                                    d.sub.calc, g/cm.sup.3                                                                  4.816       4.674       2.977                                         crystal  0.23 × 0.30 ×                                                                  0.16 × 0.30 ×                                                                  0.26 × 0.44 ×                     size (mm)                                                                               0.31        0.50        0.52                                          temp. (°C.)                                                                      20          23          23                                            radiation                                                                               Mo Kα Mo Kα Mo Kα                                   μ(Mo Kα),                                                                      328.89      352.34      76.59                                         cm.sup.-1                                                                      scan mode                                                                               ω     ω-2θ                                                                           ω-2θ                              scan speed,                                                                             2θ = 3˜43°                                                              2           4                                             °/min                                                                            4°/min                                                                  2θ = 43˜55°                                                 2°/min                                                         2θ.sub.max, deg                                                                   55          50          50.0                                          no. of data                                                                             1087        801         497                                           collected                                                                      no. of   999         795         497                                           unique data                                                                    no. of   882         632         456                                           observed                                                                       data                                                                           (I>3.0 σ(I)                                                              no. of   69          69          46                                            variables                                                                      final    3.9/4.2     4.3/5.9     3.6/4.6                                       R/R.sub.w, %                                                                   ______________________________________                                                   (IV)        (V)                                                      ______________________________________                                         formula     Rb.sub.2 ZnSn.sub.2 S.sub.6                                                                  Cs.sub.2 MnSn.sub.2 S.sub.6                          fw          666.06        750.49                                               a, Å    6.873(2)      7.098(1)                                             b, Å    13.456(4)     13.729(3)                                            c, Å    7.285(2)      7.434(1)                                             α     90.0          90.0                                                 β      113.12(2)     112.57(1)                                            γ     90.0          90.0                                                 Z, V, Å.sup.3                                                                          2, 619.7(3)   2, 668.9(4)                                          space group P2.sub.1 (#4) P2.sub.1 (#4)                                        d.sub.calc, g/cm.sup.3                                                                     3.569         3.726                                                crystal size, mm                                                                           0.42 × 0.40 × 0.14                                                               0.43 × 0.42 × 0.15                       temperature (°C.)                                                                   -90           -95                                                  radiation   Mo Kα   Mo Kα                                          μ(Mo Kα), cm.sup.-1                                                               145.04        107.99                                               scan mode   ω-2θ                                                                             ω-2θ                                     scan speed, °/min                                                                   8             4                                                    2θ.sub.max, deg                                                                      50.0          55.0                                                 no. of data 1247          1737                                                 collected                                                                      no. of unique                                                                              1154          1619                                                 data                                                                           no. of observed                                                                            1044          1560                                                 data                                                                           (I>3.0 σ(I))                                                             no. of variables                                                                           100                                                                final R/R.sub.w, %                                                                         2.7/3.4       6.29/8.36                                            ______________________________________                                    

                  TABLE 2                                                          ______________________________________                                         Positional Parameters and Equivalent Isotropic                                 Displacement Values (Å.sup.2).sup.a for K.sub.2 Hg.sub.3 Sn.sub.2          S.sub.8 with Estimated                                                         Standard Deviations in Parentheses                                             atom     x          y         z       B(eq)                                    ______________________________________                                         Hg(1)    0.5        1.0000    0.4894(2)                                                                              1.06(4)                                  Hg(2)    0.25473(5) 0.5396(1) 0.6491  1.47(3)                                  Sn       0.36675(7) 0.7856(2) 0.3366(2)                                                                              0.39(5)                                  K        0.3835(3)  0.7960(7) 0.8424(9)                                                                              1.7(2)                                   S(1)     0.2674(2)  0.7891(6) 0.4952(9)                                                                              1.1(2)                                   S(2)     0.4697(3)  0.7709(6) 0.4967(9)                                                                              0.9(2)                                   S(3)     0.3751(3)  0.4894(6) 0.6835(8)                                                                              0.9(2)                                   S(4)     0.1330(2)  0.5843(6) 0.6806(7)                                                                              0.6(2)                                   ______________________________________                                    

                  TABLE 3                                                          ______________________________________                                         Positional Parameters and Equivalent Isotropic                                 Displacement Values (Å.sup.2).sup.a for K.sub.2 Hg.sub.3 Ge.sub.2          S.sub.8 with Estimated                                                         Standard Deviations in Parentheses                                             atom     x          y         z       B(eq)                                    ______________________________________                                         Hg(1)    0.5        0         0.5251(5)                                                                              1.51(8)                                  Hg(2)    0.74494(8) 0.4552(1) 0.3587  1.95(6)                                  Ge       0.6351(2)  0.2110(4) 0.6719(5)                                                                              0.9(2)                                   K        0.6125(5)  0.198(1)  0.161(1)                                                                               2.2(4)                                   S(1)     0.7298(5)  0.2079(8) 0.527(2)                                                                               1.6(4)                                   S(2)     0.5388(5)  0.2330(8) 0.520(2)                                                                               1.6(4)                                   S(3)     0.6234(5)  0.518(1)  0.314(1)                                                                               1.2(4)                                   S(4)     0.8681(4)  0.4026(9) 0.322(1)                                                                               1.0(3)                                   ______________________________________                                          .sup.a B(eq) = 4/3(a.sup.2 β11 + b.sup.2 β22 + c.sup.2 β33      + ab(cosγβ12 + ac(cosβ)β13 + bc(cosα)β23)

                  TABLE 4                                                          ______________________________________                                         Positional Parameters and Equivalent Isotropic                                 Displacement Values (Å.sup.2).sup.a for K.sub.6 Zn.sub.4 Sn.sub.5          S.sub.17 with Estimated                                                        Standard Deviations in Parentheses                                             atom   x         y          z        B(eq)                                     ______________________________________                                         Sn(1)  1/2       1/2          0       1.50(7)                                  Sn(2)  0.7756(1) 1/2        -0.0260(1)                                                                               1.53(6)                                  Zn     1.0000    0.3611(2)  -0.1095(2)                                                                               1.4(1)                                   K(1)   1.0000    1/2          1/4     2.9(3)                                   K(2)   0.7585(4) 1.2585     -1/4      3.8(2)                                   K(3)   1/2       1/2          1/2    29(3)                                     S(1)   1.0000    1/2        -1/4      1.1(2)                                   S(2)   0.7174(4) 1/2        -0.2589(6)                                                                               2.3(2)                                   S(3)   0.8628(2) 0.3578(3)    0.0326(4)                                                                              1.9(1)                                   S(4)   0.6428(4) 1/2          0.1434(6)                                                                              2.9(3)                                   ______________________________________                                          .sup.a B(eq) = 4/3(a.sup.2 β11 + b.sup.2 β22 + c.sup.2 β33      + ab(cosγ)β12 + ac(cosββ13 + bc                           (cosα)β23).                                                   

                  TABLE 5                                                          ______________________________________                                         Positional Parameters and Equivalent Isotropic                                 Displacement Values (Å.sup.2).sup.a for Rb.sub.2 ZnSn.sub.2 S.sub.6        with Estimated                                                                 Standard Deviations in Parentheses                                             atom   x         y           z        B (eq)                                   ______________________________________                                         Sn(1)  0.3925(1)   0.2663      0.3662(1)                                                                             0.59(3)                                  Sn(2)  0.2806(1) -0.0123(1)    0.3020(1)                                                                             0.62(3)                                  Rb(1)  0.0580(2)   0.2402(1)   0.7341(2)                                                                             1.89(6)                                  Rb(2)  0.6596(2)   0.0824(1)   0.0081(2)                                                                             1.60(6)                                  Zn     0.8413(2)   0.3966(2)   0.2470(2)                                                                             0.79(6)                                  S(1)   0.4872(5)   0.3414(3)   0.1226(5)                                                                             1.1(1)                                   S(2)   0.5523(6)   0.3307(3)   0.7017(5)                                                                             1.2(1)                                   S(3)   0.1305(5)   0.0271(3) -0.0431(5)                                                                              0.9(1)                                   S(4)   0.0233(5)   0.2481(3)   0.2507(6)                                                                             1.1(1)                                   S(5)   0.9758(5)   0.4756(3)   0.5606(5)                                                                             1.3(1)                                   S(6)   0.5611(6)   0.1038(3)   0.4693(6)                                                                             1.2(1)                                   ______________________________________                                    

                  TABLE 6                                                          ______________________________________                                         Positional parameters and Equivalent Isotropic                                 Displacement Values (Å.sup.2).sup.a for Cs.sub.2 MnSn.sub.2 S.sub.6        with Estimated                                                                 Standard Deviations in Parentheses.                                            atom   x         y           z        B (eq)                                   ______________________________________                                         Sn(1)  0.3966(3)   0.2663      0.3626(3)                                                                             0.53(6)                                  Sn(2)  0.2862(3) -0.0082(2)    0.3222(3)                                                                             0.50(6)                                  Cs(1)  0.0544(3)   0.2358(2)   0.7311(3)                                                                             1.45(7)                                  Cs(2)  0.6606(3)   0.0778(2)   0.0209(3)                                                                             1.32(7)                                  Mn     0.8412(7)   0.3933(4)   0.2286(7)                                                                             0.7(1)                                   S(1)   0.495(1)    0.3300(7)   0.118(1)                                                                              1.2(3)                                   S(2)   0.542(1)    0.3419(6)   0.681(1)                                                                              1.2(3)                                   S(3)   0.138(1)    0.0257(6) -0.015(1)                                                                               1.0(2)                                   S(4)   0.041(1)    0.2498(6)   0.249(1)                                                                              1.0(3)                                   S(5)   0.958(1)    0.4841(7)   0.537(1)                                                                              1.2(3)                                   S(6)   0.554(1)    0.1088(6)   0.481(1)                                                                              1.0(2)                                   ______________________________________                                          .sup.a B(eq) = 4/3(a.sup.2 β11 + b.sup.2 β22 + c.sup.2 β33      + ab(cosγ)β12 + ac(cosβ)β13 + bc                          (cosα)β23).                                                   

Examples 1 to 5 show the feasibility of using molten salts as synthetic tools for the chalcogenide quaternary compounds of the present invention. This suggests molten salts provide good homogeneous reaction media for mixed metal systems. (Sn₂ S₆)⁴⁻ and (SnS₄)⁴⁻, which can be isolated as separate anions from the A₂ S_(x) fluxes, are potentially good building blocks to construct quaternary structures. The chalcogenide compounds of Examples 1 to 5 also contain (MS₄)⁴⁻ (M=Sn or Ge) linked by linear HgS₂ or tetrahedral MQ4 units (M=Hg, Zn, Mn; Q=S).

The formation of K₂ Hg₃ Sn₂ S₈ (I) and K₂ Hg₃ Ge₂ S₈ (II) is an example of the fact that Sn and Ge often undergo similar chemistry since they belong to the same group in the periodic table. Other examples are the formation of discrete anions such as (MQ₄)⁴⁻, (M₂ Q₆)⁴⁻, and (M₄ Q₁₀)⁴⁻,⁵,6 where M=Ge, Sn; Q=S, Se. The radius of Sn⁴⁺ is about 0.2 Å larger than that of Ge⁴⁺. The three dimensional structures of (I) and (II) must be flexible enough to tolerate the large size difference of Ge and Sn.

Structures of K₂ Hg₃ Sn₂ S₈ (I) and K₂ Hg₃ Ge₂ S₈ (II) (Examples 1 and 2)

Chalcogenide compounds (I) and (II) are isostructural with Sn and Ge occupying the same metal sites. They have complicated three-dimensional structures made up with tetrahedral MS₄ (M=Sn in (I) and Ge in (II)), linear HgS₂ and "saddle-like" HgS₄ which contains two short and two long Hg-S bonds. The structure of chalcogenide compound (I) or (II) is shown in FIG. 1. The structures of chalcogenide (I) and (II) are non-centrosymmetric. This can be readily seen by the fact that all S(1)-Hg(2)-S(1) and S(3)-M-S(4) (M=Sn or Ge) angles are pointed to the same direction, <001>, see FIG. 1. If the two long Hg(2)-S(1) bonds of the saddle-like HgS₄ units are not considered as bonds, the complicated three-dimensional framework can be simplified to a two-dimensional sheet, as shown in Scheme I. ##STR1## The two-dimensional sheet is constructed by rows of parallel S(3)-Hg(2)-S(4) fragments linked alternately by MS₄ (M=Sn or Ge) tetrahedra in a corner-sharing fashion to form wave-like chains running in a sequence of S(3)-Hg(2)-S(4)-M-S(3)-Hg(2) . These parallel wave-like chains are then extended to (Hg₃ M₂ S₈)²⁻ sheets by connecting the S(2) atoms of MS₄ tetrahedra through linear S(2)-Hg(1)-S(2) units. These two-dimensional sheets are further expanded to three-dimensional networks via weak Hg(2)-S(1) bondings between two adjacent (Hg₃ M₂ S₈)²⁻ sheets. This forms parallel tunnels, enclosed by edge-sharing 20-membered rings which contains edges of four MS₄ tetrahedra, two linear HgS₂ and four saddle-like HgS₄ units, running along the <011> crystallographic direction. K⁺ cations are located in the tunnels, as shown in FIG. 2.

A comparison of the selected bond distances and bond angles between chalcogenide compounds (I) and (II) are given in Table 7.

                                      TABLE 7                                      __________________________________________________________________________     Comparison of Selected bond Distances (Å) and Angles                       (deg) of K.sub.2 Hg.sub.3 Sn.sub.2 S.sub.8 (I) and K.sub.2 Hg.sub.3            Ge.sub.2 S.sub.8 (II) with Standard                                            Deviations in Parentheses                                                                (I)   (II)            (I)   (II)                                     __________________________________________________________________________     Selected Bond Distances (Å)                                                Hg(1)--S(2)                                                                              2.331(6)                                                                             2.361(8)                                                                             mean(M--S)                                                                               2.39(3)                                                                              2.22(3)                                  Hg(2)--S(1)                                                                              2.787(7)                                                                             2.778(9)                                                                             K--S(1)   3.217(8)                                                                             3.23(1)                                  Hg(2)--S(1)                                                                              2.818(6)                                                                             2.85(1)                                                                              K--S(2)   3.37(1)                                                                              3.32(2)                                  Hg(2)--S(3)                                                                              2.419(5)                                                                             2.436(9)                                                                             K--S(2)   3.215(8)                                                                             3.20(1)                                  Hg(2)--S(4)                                                                              2.432(5)                                                                             2.436(9)                                                                             K--S(3)   3.304(9)                                                                             3.34(1)                                  M--S(1)   2.356(6)                                                                             2.18(1)                                                                              K--S(3)   3.452(9)                                                                             3.38(1)                                  M--S(2)   2.426(6)                                                                             2.25(1)                                                                              K--S(4)   3.163(9)                                                                             3.16(1)                                  M--S(3)   2.390(7)                                                                             2.22(1)                                                                              K--S(4)   3.545(9)                                                                             3.46(1)                                  M--S(4)   2.377(6)                                                                             2.23(1)                                                                              mean(K--S)                                                                               3.32(14)                                                                             3.30(11)                                 Selected Bond Angles (deg)                                                     S(3)--M--S(4)                                                                            113.6(2)                                                                             113.0(4)                                                                             S(1)--M--S(4)                                                                            109.2(2)                                                                             110.1(4)                                 S(2)--Hg(1)--S(2)                                                                        177.0(4)                                                                             177.8(7)                                                                             S(2)--M--S(3)                                                                            107.1(2)                                                                             107.3(4)                                 S(1)--Hg(2)--S(1)                                                                        124.7(3)                                                                             119.9(5)                                                                             S(2)--M--S(4)                                                                            104.9(2)                                                                             102.4(4)                                 S(1)--Hg(2)--S(3)                                                                        98.6(2)                                                                              100.8(3)                                                                             Hg(1)--S(2)--M                                                                           97.9(2)                                                                              99.1(4)                                  S(1)--Hg(2)--S(4)                                                                        88.8(2)                                                                              89.3(3)                                                                              Hg(2)--S(3)--M                                                                           99.8(2)                                                                              101.0(4)                                 S(1)--Hg(2)--S(3)                                                                        91.5(2)                                                                              91.5(3)                                                                              Hg(2)--S(4)--M                                                                           102.0(2)                                                                             102.5(3)                                 S(1)--Hg(2)--S(4)                                                                        93.3(2)                                                                              94.3(3)                                                                              Hg(2)--S(1)--Hg(2)                                                                       122.8(3)                                                                             117.6(5)                                 S(3)--Hg(2)--S(4)                                                                        166.8(2)                                                                             163.8(3)                                                                             Hg(2)--S(1)--M                                                                           108.9(2)                                                                             110.8(4)                                 S(1)--M--S(2)                                                                            111.5(2)                                                                             112.0(4)                                                                             Hg(2)--S(1)--M                                                                           113.6(2)                                                                             115.2(3)                                 S(1)--M--S(3)                                                                            110.5(2)                                                                             111.7(4)                                                       __________________________________________________________________________      *M = Sn (I) or Ge (II)                                                   

The average Sn-S distance is 2.39 (3) Å while the average Ge-S distance is shorter at 2.22 (3) Å. The S-M-S angles are close to those of a perfect tetrahedron. There are two distinct Hg atoms. Hg(1) adopts linear coordination with the Hg(1)-S(2) distances at 2.331(6) Å and 2.361(8) Å, the S(2)-Hg(1)-S(2) angles at 177.0(4)° and 177.8 (7)° for chalcogenide compounds (I) and (II), respectively. The linear geometry of HgS₂ is common for thiomercurates and has been found in HgS (cinnabar)¹², BaHgS₂ ¹³ A₂ Hg₃ S₄ (A=Na, K) and K₂ Hg₆ S₇ ^(2g). The Hg-S distances and S-Hg-S angles found in chalcogenide compounds (I) and (II) are comparable to those found in these compounds. Hg(2) is four coordinated and adopts a saddle-like geometry which has two short and two long Hg-S bonds, the former averaging 2.426 (9) Å and 2.436(9)Å, the latter averaging 2.80(2) Å and 2.81(5) Å for chalcogenide compounds (I) and (II), respectively. This coordination type of HgS₄ is novel and has not been observed in other thiomercurates. The angles between the two short Hg-S bonds in (I) and (II) are 166.8 (2)° and 163.8(3) Å respectively, which still possess some character of linearity. The deviations from perfect linearity are caused by the formation of two long Hg-S bonds between Hg(2) and S(1) atoms which are actually shared with tetrahedral MS₄ (M=Sn or Ge). The two short Hg-S bond distances fall between those in normal linear HgS₂ (ca. 2.35Å) and tetrahedral HgS₄ (ca. 2.55Å) . Therefore, the coordination geometry of Hg(2) may be considered as an intermediate between tetrahedral HgS₄ and linear HgS₂ having short contacts with two S atoms.

The K⁺ cations of chalcogenide compounds (I) and (II) are both surrounded by seven sulfur atoms with the average K⁺. . . S distances at 3.32(14) Åand 3.30(11) Å respectively.

Structure of K₆ Zn₄ Sn₅ S₁₇ (III) --Example 3

Chalcogenide compound (III) has a complicated three-dimensional structure which is made up by linking tetrahedrally coordinated Sn⁴⁺ ions and (Zn₄ Sn₄ S₁₇)¹⁰⁻ clusters via sulfur atoms in a vertex-sharing fashion, as shown in FIG. 3. The (Zn₄ Sn₄ S₁₇)¹⁰⁻ cluster, shown in FIG. 4, actually features fused boat-form six-membered rings. It contains a sulfur atom at its center tetrahedrally bonded to four Zn atoms. The four triangular faces of the (SZn₄)⁶⁺ tetrahedron are then capped with four (SnS₄)⁴⁻ tetrahedra in a face-sharing fashion. The resulting (Zn₄ Sn₄ S₁₇)¹⁰⁻ clusters possess pseudo-tetrahedral site symmetry and are practically functioning as huge tetrahedral (MS₄)¹⁰⁻ (M=(Zn₄ Sn₄ S₁₃)) building blocks. The linkage of Sn⁴⁺ and (Zn₄ Sn₄ S₁₇)¹⁰⁻ generates three different types of tunnels in which charge balancing potassium cations are located: type (a) is formed by connecting Sn⁴⁺ and (MS₄)¹⁰⁻ tetrahedra in a helix way along a 2₁ screw axis in the <001> crystallographic direction (see FIG. 3); type (b) is wide and flat and is enclosed by four (M/SnS₄) chains running along <010> or <100> axis (see FIG. 5); type (c) is formed by connecting Sn⁴⁺ and (MS₄)¹⁰⁻ tetrahedra in a helix way along a pseudo-3₁ screw axis in the <010> or <110> direction (see FIG. 6). (III) crystallizes in a noncentrosymmetric tetragonal space group. Four fold improper rotation axes pass through the Sn(1) atom of the (SnS₄)⁴⁻ units and S(1) atoms at the center of (Zn₄ Sn₄ S₁₇)¹⁰⁻ clusters. The absence of center of symmetry is clearly visible in FIG. 5.

Selected bond distances and angles are given in Table 8. The average Sn-S and Zn-S distances are 2.40(3) Å and 2.339(9) Å, respectively. The S-M-S angles do not deviate very much from those of a perfect tetrahedron. Only slight deviations occur at Sn(1) and S(1) and reduce the site symmetry from T_(d) to S₄.

There are three crystallographically distinct potassium cations. K(1) is sandwiched by two (Zn₄ Sn₄ S₁₇)¹⁰⁻ clusters, each providing four S(3) atoms for coordination. K(2) is located at the intersection of two sets of tunnels running along the crystallographic <001> axis and <010> (or <110>) axis. K(3) is located between two K(2)'s in the same tunnels running along <110>or <110> axis, as shown in FIG. 6. All potassium cations are eight-coordinated. The average K-S for K(1) and K(2) is normal at 3.37(12) Å. K(3) is located in a wider cavity inside the tunnels, surrounded by four S(2) atoms from four (Zn₄ Sn₄ S₁₇)¹⁰⁻ clusters and four S(4) atoms from two (SnS₄)⁴⁻ tetrahedra. The size of the cavity is however too large for a K⁺ cation (the center is 3.784Å to S(2) and 3.944Å to S(4)). The crystallographic data suggests that K(3) is not localized at a certain position but "rattling" around the center of the cavity.

                                      TABLE 8                                      __________________________________________________________________________     Selected Bond Distances (Å) and Angles (deg) for K.sub.6 Zn.sub.4          Sn.sub.5 S.sub.17                                                              with Standard Deviations in Parentheses                                        __________________________________________________________________________     Selected Bond Distances (Å)                                                Sn(1)--S(4)                                                                               2.402(6) × 4                                                                     K(1)--S(3)                                                                                3.431(4) × 8                               Sn(2)--S(2)                                                                               2.372(6)                                                                               K(2)--S(2)                                                                                3.381(1) × 2                               Sn(2)--S(3)                                                                               2.369(4) × 2                                                                     K(2)--S(3)                                                                                3.358(4) × 2                               Sn(2)--S(4)                                                                               2.448(6)                                                                               K(2)--S(3)                                                                                3.116(5) × 2                               mean(Sn--S)                                                                               2.40(3) mean(K(1,2)--S)                                                                           3.37(12)                                         Zn--S(1)   2.342(2)                                                                               K(3)--S(2)                                                                                3.784(6) × 4                               Zn--S(2)   2.350(6)                                                                               K(3)--S(4)                                                                                3.944(5) × 4                               Zn--S(3)   2.332(4) × 2                                                                     mean(K(3)--S)                                                                             3.86(11)                                         mean(Zn--S)                                                                               2.339(9)                                                            Selected Bond Angles (deg)                                                     S(4)--Sn(1)--S(4)                                                                        109.1(1) × 4                                                                      S(1)--Zn--S(3)                                                                           110.6(1) × 2                                S(4)--Sn(1)--S(4)                                                                        110.2(3) × 2                                                                      S(2)--Zn--S(3)                                                                           107.2(1) × 2                                S(2)--Sn(2)--S(3)                                                                        113.3(1) × 2                                                                      S(3)--Zn--S(3)                                                                           108.5(2)                                          S(2)--Sn(2)--S(4)                                                                        111.7(2) Zn--S(1)--Zn                                                                             109.30(5) × 4                               S(3)--Sn(2)--S(3)                                                                        111.8(2) Zn--S(1)--Zn                                                                             109.8(1) × 2                                S(3)--Sn(2)--S(4)                                                                        102.9(1) × 2                                                                      Sn(2)--S(2)--Zn                                                                          102.6(2)                                          S(3)--Sn(2)--S(4)                                                                        102.9(1) Sn(2)--S(3)--Zn                                                                          104.9(1)                                          S(1)--Zn--S(2)                                                                           112.5(2) Sn(1)--S(4)--Sn(2)                                                                       103.6(2)                                          __________________________________________________________________________

Rb₂ ZnSn₂ S₆ (IV) and Cs₂ MnSn₂ S₆ (V) (Examples 4 and 5)

Chalcogenide compounds (IV) and (V) are isostructural, forming a new three-dimensional structure type with corner-sharing tetrathiometalates as building blocks, as shown in FIG. 7. In order to have a better view of the structure, it can be divided into layers perpendicular to the b-axis, as shown in FIG. 8. Each layer is related to its adjacent layer by a two-fold improper rotation symmetry parallel to the b-axis, thus resulting in a noncentrosymmetric space group (P2₁, #4). A such discrete layer consists of slightly twisted boat-shaped ((MSn₂ S₃)S₆)⁴⁻ (M=Mn or Zn) six-membered rings connected by sharing four of their six terminal sulfur atoms. The remaining two axial sulfur atoms, S(6), link the adjacent layers above and below, extending to three-dimensional frameworks and forming parallel tunnels running along <100> and <001> axes. These tunnels are narrow in width (˜3.2Å) so free movement of Cs⁺ or Rb⁺ cations along the tunnels is not expected. The charge balancing cations are located at the cavities near the boundary of the tunnels.

Selected bond distances and angles for chalcogenide compounds (IV) and (V) are given in Tables 9 and 10 respectively.

                  TABLE 9                                                          ______________________________________                                         Selected Bond Distances (Å) and Angles (deg) for                           Rb.sub.2 ZnSn.sub.2 S.sub.6 with Standard Deviations in                        ______________________________________                                         Parentheses                                                                    Selected Bond Distances (Å)                                                Sn(1)--S(1)                                                                                2.346(4) Rb(1)--S(2)    3.704(4)                                   Sn(1)--S(2)                                                                                2.413(4) Rb(1)--S(2)    3.602(4)                                   Sn(1)--S(4)                                                                                2.352(4) Rb(1)--S(3)    3.235(4)                                   Sn(1)--S(6)                                                                                2.451(4) Rb(1)--S(4)    3.437(4)                                   Sn(2)--S(2)                                                                                2.409(4) Rb(1)--S(5)    3.376(5)                                   Sn(2)--S(3)                                                                                2.373(4) Rb(1)--S(6)    3.686(4)                                   Sn(2)--S(5)                                                                                2.349(4) Rb(2)--S(1)    3.419(4)                                   Sn(2)--S(6)                                                                                2.408(4) Rb(2)--S(3)    3.585(4)                                   mean(Sn--S)                                                                                2.39(4)  Rb(2)--S(3)    3.481(4)                                   Zn--S(1)    2.359(4) Rb(2)--S(4)    3.298(4)                                   Zn--S(3)    2.357(4) Rb(2)--S(5)    3.469(4)                                   Zn--S(4)    2.352(4) Rb(2)--S(6)    3.690(5)                                   Zn--S(5)    2.355(4) Rb(2)--S(6)    3.724(5)                                   mean(Zn--S)                                                                                2.356(3) mean(Rb--S)    3.51(16)                                   Rb(1)--S(1)                                                                                3.466(4)                                                           Selected Bond Angles (deg)                                                     S(1)--Sn(1)--S(2)                                                                         117.4(1)  S(1)--Zn--S(3)                                                                               108.7(1)                                    S(1)--Sn(1)--S(4)                                                                         110.8(1)  S(1)--Zn--S(4)                                                                               101.6(1)                                    S(1)--Sn(1)--S(6)                                                                         112.2(1)  S(1)--Zn--S(5)                                                                               117.9(1)                                    S(2)--Sn(1)--S(4)                                                                         113.5(1)  S(3)--Zn--S(4)                                                                               117.7(1)                                    S(2)--Sn(1)--S(6)                                                                          92.2(1)  S(3)--Zn--S(5)                                                                               100.2(2)                                    S(4)--Sn(1)--S(6)                                                                         109.3(1)  S(4)--Zn--S(5)                                                                               111.6(1)                                    S(2)--Sn(2)--S(3)                                                                         101.3(1)  Sn(1)--S(1)--Zn                                                                              113.3(1)                                    S(2)--Sn(2)--S(5)                                                                         112.6(1)  Sn(1)--S(2)--Sn(2)                                                                           109.5(1)                                    S(2)--Sn(2)--S(6)                                                                         106.5(1)  Sn(2)--S(3)--Zn                                                                              113.1(2)                                    S(3)--Sn(2)--S(5)                                                                         112.3(1)  Sn(1)--S(4)--Zn                                                                              114.2(2)                                    S(3)--Sn(2)--S(6)                                                                         108.6(1)  Sn(2)--S(5)--Zn                                                                              111.7(1)                                    S(5)--Sn(2)--S(6)                                                                         114.5(1)  Sn(1)--S(6)--Sn(2)                                                                           103.6(1)                                    ______________________________________                                    

                  TABLE 10                                                         ______________________________________                                         Selected Bond Distances (Å) and Angles (deg) of                            Cs.sub.2 MnSn.sub.2 S.sub.6 with Standard Deviations in                        ______________________________________                                         Parentheses                                                                    Selected Bond Distances (Å)                                                Sn(1)--S(1)                                                                                2.349(9) Cs(1)--S(2)    3.80(1)                                    Sn(1)--S(2)                                                                                2.424(8) Cs(1)--S(3)    3.373(8)                                   Sn(1)--S(4)                                                                                2.342(8) Cs(1)--S(4)    3.558(9)                                   Sn(1)--S(6)                                                                                2.439(8) Cs(1)--S(4)    3.888(9)                                   Sn(2)--S(2)                                                                                2.396(8) Cs(1)--S(5)    3.66(1)                                    Sn(2)--S(3)                                                                                2.361(8) Cs(1)--S(5)    3.97(1)                                    Sn(2)--S(5)                                                                                2.343(8) Cs(1)--S(6)    3.746(8)                                   Sn(2)--S(6)                                                                                2.423(8) Cs(2)--S(1)    3.815(9)                                   mean(Sn--S)                                                                                2.38(4)  Cs(2)--S(1)    3.604(9)                                   Mn--S(1)    2.43(1)  Cs(2)--S(3)    3.686(9)                                   Mn--S(3)    2.457(9) Cs(2)--S(3)    3.570(9)                                   Mn--S(4)    2.401(9) Cs(2)--S(4)    3.498(8)                                   Mn--S(5)    2.459(9) Cs(2)--S(5)    3.598(8)                                   mean(Mn--S)                                                                                2.44(3)  Cs(2)--S(6)    3.795(9)                                   Cs(1)--S(1)                                                                                3.581(9) Cs(2)--S(6)    3.816(9)                                   Cs(1)--S(2)                                                                                3.904(9) mean(Cs--S)    3.70(16)                                   Selected Bond Angles (deg)                                                     S(1)--Sn(1)--S(2)                                                                         117.0(3)  S(1)--Mn--S(3)                                                                               110.5(3)                                    S(1)--Sn(1)--S(4)                                                                         110.7(3)  S(1)--Mn--S(4)                                                                               103.0(3)                                    S(1)--Sn(1)--S(6)                                                                         112.1(3)  S(1)--Mn--S(5)                                                                               115.5(3)                                    S(2)--Sn(1)--S(4)                                                                         113.1(3)  S(3)--Mn--S(4)                                                                               117.8(3)                                    S(2)--Sn(1)--S(6)                                                                          93.6(3)  S(3)--Mn--S(5)                                                                                98.4(3)                                    S(4)--Sn(1)--S(6)                                                                         109.0(3)  S(4)--Mn--S(5)                                                                               112.3(3)                                    S(2)--Sn(2)--S(3)                                                                         100.3(3)  Sn(1)--S(1)--Mn                                                                              115.7(3)                                    S(2)--Sn(2)--S(5)                                                                         115.6(3)  Sn(1)--S(2)--Sn(2)                                                                           112.7(3)                                    S(2)--Sn(2)--S(6)                                                                         105.5(3)  Sn(2)--S(3)--Mn                                                                              115.3(3)                                    S(3)--Sn(2)--S(5)                                                                         112.2(3)  Sn(1)--S(4)--Mn                                                                              118.2(3)                                    S(3)--Sn(2)--S(6)                                                                         109.4(3)  Sn(2)--S(5)--Mn                                                                              113.4(3)                                    S(5)--Sn(2)--S(6)                                                                         113.0(3)  Sn(1)--S(6)--Sn(2)                                                                           104.3(3)                                    ______________________________________                                    

The average Sn-S distances for (IV) and (V) are similar at 2.38(4) Å and 2.39(4) Å respectively and are comparable to those of other (SnS₄)⁴⁻ containing compounds. The average Mn-S distance (2.44(3) Å) is significantly larger than that of Zn-S (2.356(3) Å). This explains why the lattice of (V) is stabilized by larger Cs⁺ cations while chalcogenide compound (IV) is stabilized by Rb⁺ cations. The coordination environments for Cs⁺ and Rb⁺ ions in chalcogenide compounds (V) and (VI) respectively are similar with average Cs⁺. . . S distance of 3.70(16) Å and average Rb⁺. . . S distance of 3.61(22) Å. The corresponding S-Sn-S and S-M-S (M=Zn or Mn) angles in (IV) and (V) are comparable and deviate from those of a perfect tetrahedra.

Even though it is possible that Sn and Mn or Zn are disordered at metal sites due to their similarity of ionic radii, their reasonable temperature factors based on the structure refinements of crystallographic data indicate an ordered model. The perfect paramagnetic behavior of (V) also suggests the current ordered model in which Mn atoms are separated by a Sn and two S atoms, resulting in negligible magnetic dipole-dipole coupling due to long Mn.sup.. . . Mn distances (7.098(1) Å, 7.434(1) Å and 7.842(1) Å). (IV) is diamagnetic because both Sn⁴⁺ and Zn²⁺ do not contain unpaired electrons.

Spectroscopy Magnetic Susceptibility Measurements Cs₂ MnSn₂ S₆ (V)--Example 5

Measurements of magnetization versus applied magnetic field were performed at 5° K. and 300° K. At both temperatures, the magnetic susceptibilities of the sample were magnetic field independent up to 5000 Gauss, as shown in FIG. 9. Variable temperature magnetic susceptibility data were collected at a magnetic field of 5000 Gauss with an ascending temperature ramp from 5° K. to 300° K. FIGS. 10A and 10B show the relationship between the reciprocal of molar magnetic susceptibilities and temperatures. It exhibits Curie-Weiss behavior (χ=C/(T+θ), where χ is magnetic susceptibility, C is Curie constant, T is the experimental temperature and θ is Weiss temperature, above the Neel temperature of 9° K. at which antiferromagnetic transition occurs. The slope of the straight line in the Curie-Weiss region gives the value C =4.21 (°K-emu-mol⁻¹). The interception at the temperature axis from the extrapolated straight line give a θ value of -22.7° K. The effective magnetic moment, μeff, related to the number of unpaired electrons, is 5.78 BM, which is calculated using the equation: χ=(Nβ² μ²)/(3k(T+θ)) or μ=2.828(χ(T+θ)).sup. 1/2 when N, β and k are substituted. (N: Avogrado's number; β: Bohr magneton; k=Boltzmann's constant). The theoretical magnetic moment, μ_(s), based on electron spin only, is given by μ_(s) =g(S+(S+1).sup. 1/2, where g=gyromagnetic ratio ˜2.00, S=the sum of the spin quantum numbers for unpaired electrons. The calculated μ_(s), value, 5.92 BM, based on high spin Mn²⁺ ions with S=5/2, is consistent with the observed result.

The UV-Vis-Near IR solid state spectra of chalcogenide compounds (I)˜(V) exhibit steep absorption edges from which optical band gaps can be derived. The spectra are shown in FIG. 11. The summary of their optical band gaps are given in Table 11. The band gaps are all consistent with the colors. These results suggest all these compounds are semiconductors in nature.

The vibrational spectra and absorption frequencies for (I)˜(V) are given in FIG. 12 and Table 12 respectively.

                  TABLE 11                                                         ______________________________________                                         Summary of the Optical Band Gaps (eV) for K.sub.2 Hg.sub.3 Sn.sub.2            S.sub.8 (I),                                                                   K.sub.2 Hg.sub.3 Ge.sub.2 S.sub.8 (II), K.sub.6 Zn.sub.4 Sn.sub.5              S.sub.17 (III),                                                                Rb.sub.2 ZnSn.sub.2 S.sub.6 (IV), Cs.sub.2 MnSn.sub.2 S.sub.6 (V),             Rb.sub.2 Hg.sub.3 Sn.sub.2 S.sub.8 (VI), Rb.sub.2 Hg.sub.3 Ge.sub.2            S.sub.8 (VII).                                                                          Eg                      Eg                                            compound (eV)   color   compound (eV) color                                    ______________________________________                                         K.sub.2 Hg.sub.3 Sn.sub.2 S.sub.8                                                       2.39   bright  Cs.sub.2 MnSn.sub.2 S.sub.6                                                             2.58 light brown                                              yellow                                                         K.sub.2 Hg.sub.3 Ge.sub.2 S.sub.8                                                       2.64   light   Rb.sub.2 Hg.sub.3 Sn.sub.2 S.sub.8                                                      2.40 bright yellow                                            yellow                                                         K.sub.6 Zn.sub.4 Sn.sub.5 S.sub.17                                                      2.94   white   Rb.sub.2 Hg.sub.3 Ge.sub.2 S.sub.8                                                      2.65 light yellow                             Rb.sub.2 ZnSn.sub.2 S.sub.6                                                             3.00   white                                                          ______________________________________                                    

                  TABLE 12                                                         ______________________________________                                         Summary of Absorption Frequencies (cm.sup.-1) of Vibrational                   Spectra for (I)˜(V).sup.a                                                compound  frequency (cm.sup.-1)                                                ______________________________________                                         K.sub.2 Hg.sub.3 Sn.sub.2 S.sub.8                                                        383(s), 356(sh), 345(s), 316(w), 296(m), 169(m)                      K.sub.2 Hg.sub.2 Ge.sub.2 S.sub.8                                                        421(s), 393(m), 377(s), 371(sh), 353(m), 312(m),                               297(sh), 211(sh), 198(s), 148(w), 134(w)                             K.sub.6 Zn.sub.4 Sn.sub.5 S.sub.17                                                       387(s), 361(m), 342(s), 307(w), 278(s), 262(sh),                               153(m)                                                               Rb.sub.2 ZnSn.sub.2 S.sub.6                                                              390(m), 380(m), 369(s), 351(m), 332(s), 321(w),                                304(s), 275(m), 256(s), 142(s)                                       Cs.sub.2 MnSn.sub.2 S.sub.6                                                              381(s), 371(sh), 366(m), 328(s), 318(w), 299(s),                               278(m), 257(s), 139(m)                                               ______________________________________                                          .sup.a (s): strong; (m): medium; (w): weak; (sh): shoulder               

These quaternary compounds exhibit complicated spectra due to the many vibrational modes. All the absorption frequencies fall in the range between 130 cm⁻¹ and 450 cm⁻¹. This make it difficult for assignment. K₂ Hg₃ Sn₂ S₈ (I) and K₂ Hg₃ Ge₂ S₈ (II) are isostructural and therefore their vibrational spectra have similar patterns except that all the absorption bands shift, understandably, to higher frequencies in the spectrum of K₂ Hg₃ Ge₂ S₈ (II). Another pair of isostructural compounds, Rb₂ ZnSn₂ S₆ (IV) and Cs₂ MnSn₂ S₆, also exhibit similar vibrational spectra with little shift of absorption frequencies.

EXAMPLE 6 K₁.6 Rb₀.4 Hg₃ Ge₂ S₈

β-K₂ Hg₃ Ge₂ S₈ (space group C2) was synthesized using the molten salt (K_(x) S_(y)) flux reaction with the same approximate overall stoichiometry (K₈ Hg₃₋₄ Ge₂ S₄₀) as α-K₂ Hg₃ Ge₂ S₈ (space group Aba2, also acentric) but at higher temperatures or by substituting Rb for some or all of the K. Furthermore, there may be kinetic aspects to the 1st-order α→β phase transition associated with the amount of time the reaction is held at maximum temperature. Both phases with a variety of compositions have been prepared and are stable in water and air. These compounds are easily isolated in methanol and water and then dried with acetone and diethyl ether. The following table lists relevant information pertaining to syntheses of these compounds. The relative amounts of the α and β phases in two phase samples, as isolated, were estimated from visual inspection of X-ray powder diffraction plots.

    ______________________________________                                                                  estimated                                                                  cooling                                                                              phase                                               flux                   time    rate  content                                   composition  T (°C.)                                                                           at T    °C./hr                                                                        % α                                                                           % β                             ______________________________________                                         K.sub.8 Hg.sub.4 Ge.sub.2 S.sub.40                                                          400       4     d   -4    100  --                                 K.sub.8 Hg.sub.4 Ge.sub.2 S.sub.40                                                          450       4     d   -4    50   50                                 K.sub.8 Rb.sub.0.4 Hg.sub.4.3 Ge.sub.2 S.sub.43                                             400-385   5.5   d   -2    60   40                                 K.sub.6.9 Rb.sub.1.2 Hg.sub.4.2 Ge.sub.2 S.sub.40                                           400-385   5.5   d   -2    20   80                                 K.sub.6.2 Rb.sub.2.1 Hg.sub.4 Ge.sub.2 S.sub.42                                             400-385   5.5   d   -2    10   90                                 K.sub.5.6 Rb.sub.2.4 Hg.sub.4 Ge.sub.2 S.sub.40                                             400       4     d   -4    --   100                                K.sub.4.8 Rb.sub.3.2 Hg.sub.4 Ge.sub.2 S.sub.40                                             400       4     d   -4    --   100                                K.sub.8 Hg.sub.3.5 Ge.sub.2 S.sub.35                                                        500       45    hr  -4    50   50                                 K.sub.8 Hg.sub.4 Sn.sub.2 S.sub.40                                                          400       4     d   -4    100  --                                 K.sub.8 Hg.sub.4 Sn.sub.2 S.sub.40                                                          500       45    hr  -4    100  --                                 K.sub.8 Hg.sub.4 Sn.sub.2 S.sub.40                                                          460       4     d   -4    80   20                                 K.sub.6 Rb.sub.2 Hg.sub.3.5 Sn.sub.2 S.sub.40                                               approx 400                                                                               4     d   -4    100  --                                 DTA results                                                                    α-K.sub.2 Hg.sub.3 Ge.sub.2 S.sub.8                                                m.p.                  580° C.                                           recrystallization     430° C.                                 phase     XRD → β                                                            some decomposition (small amount of                                            HgS evident)                                                         α-K.sub.2 Hg.sub.3 Sn.sub.2 S.sub.8                                                m.p.                  545° C.                                           recrystallization     430° C.                                 phase + impuritiesarw. β                                                            some decomposition                                                   ______________________________________                                    

Melting points were determined by differential thermal analysis. Heating and cooling rates were 10° C./min. β-Rb₂ Hg₃ Ge₂ S₈ and β-Rb₂ Hg₃ Sn₂ S₈ both form using flux reactions with the approximate composition Rb₈ Hg₄ M₂ S₄₀ (M=Ge, Sn) at the cool end of a pyrex tube in a temperature gradient of 450°-500° C.

    ______________________________________                                         Crystal Data for K.sub.1.6 Rb.sub.0.4 Hg.sub.3 Ge.sub.2 S.sub.8                (β-K.sub.2 Hg.sub.3 Ge.sub.2 S.sub.8 type)                                ______________________________________                                         formula            K.sub.1.6 Rb.sub.0.4 Hg.sub.3 Ge.sub.2 S.sub.8              fw                 1099.71                                                     a, Å           9.649(5)                                                    b, Å           8.393(2)                                                    c, Å           9.720(2)                                                    α            90.0                                                        β             95.08(3)                                                    γ            90.0                                                        Z, V (Å.sup.3) 2,784.0(5)                                                  space group        C2 #5                                                       d.sub.calc (g/cm.sup.3)                                                                           4.658                                                       crystal size, mm   0.23 × 0.28 × 0.39                              Temp (°C.)  23                                                          radiation          Mo Kα                                                 μ (Mo Kα), cm.sup.-1                                                                     356.05                                                      secondary ext coeff (10.sup.-7)                                                                   5.3(5)                                                      scan mode          2θ-ω                                            scan speed, °/min                                                                          4                                                           2θ max, deg  50                                                          # data collected   1027                                                        # unique data      969                                                         # data observed, I >3σ (I)                                                                  883                                                         # variables        71                                                          R/R.sub.w, %       3.8/4.6                                                     R/R.sub.w, % (incl unobs refl)                                                                    4.6/4.7                                                     GOF                1.79                                                        residual e- density (pos)                                                                         +1.897                                                      residual e- density (neg)                                                                         -2.134                                                      ______________________________________                                    

    ______________________________________                                         Positional and Thermal parameters for K.sub.1.6 Rb.sub.0.4 Hg.sub.3            Ge.sub.2 S.sub.8                                                               (β-K.sub.2 Hg.sub.3 Ge.sub.2 S.sub.8 type)                                atom    x          y         z        B (eq)                                   ______________________________________                                         A       0.2124 (4) 0.1520 (6)                                                                               0.2270 (4)                                                                              1.7 (2)                                  Hg1     0          0.3592    0.5      1.94 (5)                                 Hg2     0          0.8427 (3)                                                                               0.5      2.04 (5)                                 Hg3     0          0.5229 (3)                                                                               0        1.45 (4)                                 Ge      0.2336 (2) 0.6623 (3)                                                                               0.2712 (2)                                                                              0.74 (7)                                 S1      0.7536 (5) 0.0192 (8)                                                                               0.4588 (5)                                                                              1.3 (2)                                  S2      0.2366 (5) 0.5162 (8)                                                                               0.0796 (5)                                                                              1.2 (2)                                  S3      0.4193 (5) 0.8187 (7)                                                                               0.2609 (6)                                                                              1.2 (2))                                 S4      0.5364 (6) 0.2995 (7)                                                                               0.2574 (6)                                                                              1.3 (2)                                  ______________________________________                                          atom A was refined as 80 (4) % K: 20% Rb                                 

In a similar manner the following chalcogenide compounds are prepared:

K_(2-x) Cs_(x) Hg₃ Sn₂ S₈, wherein x is 0<x<0.5;

K_(2-x) Rb_(x) Hg₃ Ge₂ S₈, wherein x is 0<x<1;

K_(2-x) Cs_(x) Ge₂ S₈, wherein 0<x<0.5;

K_(1-x) Rb_(x) Hg₃ Ge_(2-y) Sn_(y) S₈, wherein x is 0<x<1 and y is 0<x<2;

Rb₂ Hg₃ Sn₂ S₈ ;

Rb₂ Hg₃ Ge₂ S₈ ;

Cs₂ MnSn₂ Se₆ ;

Rb₂ ZnSn₂ Se₆ ;

K₆ Zn₄ Sn₅ Se₁₇ ;

K₂ Hg₃ Ge₂ Se₈ ;

K₂ Hg₃ Sn₂ Se₈ ;

K_(1-x) Rb_(x) Hg₃ Ge₂ S_(8-y) Se_(y) ; and

Rb₂ Hg₃ Sn₂ Se₈.

EXAMPLE 7 Large Crystal Growth of K₂ Hg₃ Ge₂ S₈ and K₂ Hg₃ Sn₂ S₈ Recrystallization from K₂ S₈ flux

0.20 g (1.9 ×10⁻⁴ mole) of K₂ Hg₃ Ge₂ S₈ powder was mixed with 1.9 ×10⁻⁴ mole of K₂ S₈ (0.032 g of K₂ S₃ and 0.03 g of S) and loaded in a Pyrex tube. The tube was flame-sealed under vacuum. It was heated slowly to 420° C. and kept at 420° C. for 4 days and then cooled down to 200° C. at a cooling rate of -2 C./hour. The product was isolated by washing with DMF and dried with acetone and ether under N₂.0.145 g of large (˜3 mm in size) yellow plate-like crystals were obtained. X-ray powder diffraction pattern of the crystals confirms that the yellow plates are K₂ Hg₃ Ge₂ S₈.

The mixtures of K₂ Hg₃ Ge₂ S₈ powder and K₂ S₈ in 1:3 and 1:5 ratios under the same reaction conditions also gave K₂ Hg₃ Ge₂ S₈ crystals. However, the crystal size and yield was smaller when more K₂ S₈ was used.

The reactions K₂ Hg₃ Sn₂ S₈ powder in K₂ S₈ fluxes under the same conditions also gave large K₂ Hg₃ Sn₂ S₈ crystals.

Crystal Growth From Slow Cooling

Large crystals of K₂ Hg₃ Ge₂ S₈ (up to 4×5×8 mm³) and K₂ Hg₃ Sn₂ S₈ (up to 4×4×5 mm³) have been prepared from flux reactions using the overall stoichiometry K₈ Hg₄ Mg₂ S₄₀ where M=Ge or Sn. The samples were initially heated to 500° C. over an eight hour period and then cooled to 400° C. in two hours. They were held at the 400° C. isotherm temperature for 6 days and subsequently cooled at -1° C./hr to 200° C. followed by cooling to room temperature in two hours. The initial heating to 500° C. presumably dissolved most of the seed crystals which formed as the temperature was increased. Upon isotherming and cooling, material deposited upon only a few seeds resulting in only a few large crystals. Much slower cooling (<0.1° C./hr) and/or longer isotherms can lead to still larger crystals.

It is intended that the foregoing description be only illustrative of the present invention and that the present invention be limited only by the hereinafter appended claims. 

We claim:
 1. A process for preparing a chalcogenide compound having the empirical formula

    A.sub.x B.sub.y C.sub.z D.sub.n

wherein A is selected from the group consisting of an alkali metal and a mixture of alkali metals, B is selected from the group consisting of mercury, zinc and manganese, C is a metal selected from the group consisting of germanium and tin and D is selected from the group consisting of sulfur and selenium, and wherein x is a number selected from the group consisting of 2 and 6, y is a number selected from the group consisting of 1, 3 and 4, z is a number selected from the group consisting of 2 and 5 and n is a number selected from the group consisting of 6, 8 and 17, which comprises reacting in a molten mixture ingredients selected from the group consisting of the B as an element, the C as an element, the A and the D together as an alkali metal Eide and the B and the D together as a metal Eide in molar amounts of the x, y, z or n and to produce the chalcogenide compound wherein Eide is selected from the group consisting of a sulfide or selenide.
 2. The process of claim 1 wherein the A and the D together are the alkali metal sulfide, the B and the D together are the metal sulfide.
 3. The process of claim 1 wherein the temperature is between about 200° and 800° C.
 4. The process of claim 1 wherein the chalcogenide compound prepared is washed with a degassed organic solvent.
 5. The process of claim 4 wherein the solvent is dimethyl formamide. 